High voltage pulse generator using a non-linear capacitor

ABSTRACT

The present invention is a device using a non-linear capacitor and voltage amplification effect, which can generate a pulse having a short pulse width at high voltage. The device comprises a rectification circuit for rectifying the AC input power supply, a semiconductor switch connected to one output terminal of said rectification circuit, a primary coil connected between an output of said semiconductor switch and the other output terminal of said rectification circuit, a diode in which the cathode thereof is connected to the output of said semiconductor switch, a capacitor connected between an anode of said diode and the other output terminal of said rectification circuit, a secondary coil in which one terminal thereof is connected to the anode of said diode, a non-linear capacitor connected between the other terminal of said secondary coil and the other output terminal of said rectification circuit, and a load connected in parallel across two terminals of said non-linear capacitor.

This application is a national stage filing of international application PCT/KR99/00465, filed Aug. 19, 1999 which claims priority to Korean Application Number 1998/33637 filed Aug. 19, 1998. Priority is claimed to both of these prior applications.

FIELD OF THE INVENTION

The present invention relates to a high voltage pulse generator using a non-linear capacitor or, more particularly, to a device using a voltage amplification effect of a non-linear capacitor, which can generate a pulse of a short pulse width at high voltage.

BACKGROUND ART

In many application fields of pulse power, a short high-voltage pulse having a high repetition rate is needed. A discharge-type switch is usually used in producing a short high-voltage pulse. A high-voltage pulse generating circuit using a conventional discharge-type switch is shown in FIG. 8. However, the conventional discharge-type switch has a short life span and low reliability as well as a low repetition rate. In addition, the circuit has a shortcoming of being a large size because it uses a pulse transformer and a self-saturating switch.

In contrast, a semiconductor switching component has a long life span with high reliability. However, its operational voltage range and switching time are not suitable for directly driving a pulsed power system, which requires voltage amplification (transformation) and pulse compression methods. Unfortunately, a pulse transformer and a magnetic pulse compressor have a low energy efficiency and a large size.

SUMMARY OF THE INVENTION

The present invention is, therefore, directed to providing a high-voltage pulse generating device having high efficiency with small size, using a semiconductor switching component.

The present invention also seeks to provide a high voltage pulse generating device using a semiconductor switching device with a long life span, but which does not use a pulse transformer or a magnetic pulse compressor as required by conventional circuits of the prior art.

The present invention uses the voltage amplification effect of a non-linear capacitor, which was observed during the research of BaTiO₃ ceramic capacitors by the inventors. A ceramic capacitor has a characteristic that its capacitance is generally decreased at a voltage higher than the rated value. Because reduction in capacitance is analogous to opening a switch, a non-linear capacitor may be used for pulse generation in an inductive storage system. The present invention utilizes this non-linear characteristic of a capacitor.

A high-voltage pulse generating device according to the present invention comprises a semiconductor switch connected to one output terminal of a DC power supply or rectification circuit, a primary inductor connected between an output of said semiconductor switch and the other output terminal of said rectification circuit, a diode in which the cathode thereof is connected to the output of said semiconductor switch, a capacitor connected between an anode of said diode and the other output terminal of said rectification circuit, a secondary inductor in which one terminal thereof is connected to the anode of said diode, a non-linear capacitor connected between the other terminal of said secondary inductor and the other output terminal of said rectification circuit, and a load connected in parallel across two terminals of said non-linear capacitor.

Now, an embodiment of the present invention is described as below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram describing an embodiment of the present invention.

FIG. 2 is a diagram describing the waveforms of an output voltage and the current in an inductor L₂ in an unloaded state.

FIG. 3 is a diagram describing the waveforms of an output voltage and the current in an inductor L₂ when a high-voltage discharge lamp having a non-linear characteristic is used as a load.

FIG. 4 is a diagram showing the waveforms of the voltage across the load and the current in L₂ when a pure resistor is used as a load.

FIG. 5 is a diagram showing the waveforms of voltage across C₂ and the current stored in an inductor L₁. FIG. 6 is a circuit diagram showing a stacked pulse generator where three pulse generating circuits in FIG. 1 are connected together.

FIG. 7 is a waveform diagram describing an output from a circuit in FIG. 6.

FIG. 8 is a circuit diagram describing a high-voltage pulse generating circuit using a conventional discharge switch.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a circuit diagram of an embodiment of a pulse generator in accordance with the present invention. In this embodiment, a resistor R₁ controls the charging current and a capacitor C₁ stores the primary energy (½C₁V₁ ²), where the voltage across C₁ is V₁. An inductor L₁ stores the secondary energy (½L₁I₁ ²) where the current flowing in L₁ is I₁. A capacitor C₂ stores the tertiary energy (½C₂V₂ ²), where the voltage across C₂ is V₂. An inductor L₂ causes charging in the capacitor C₂ and the capacitor C₃ in addition to facilitating the saturation of C₃. First, AC voltage from an AC power source is converted to DC voltage through a rectification circuit comprising rectification diode (1), resistor (R₁) and capacitor (C₁). In this embodiment, a voltage of about 60V is applied to capacitor (C₁). The DC voltage is converted to a pulse by control of semiconductor switch (Q₁), which is controlled by drive circuit (2).

When semiconductor switch (Q₁) is “on”, current flow through diode D₁ is prevented. Therefore, current flows only into inductor (L₁), and inductor (L₁) takes energy from low voltage capacitor (C₁) through semiconductor switch (Q₁). The current rise time in inductor L₁ is about 55 ms. The current magnitude stored in inductor (L₁) is about 130 A. Semiconductor switch (Q₁) is used as a first open switch having a rated voltage of about 1,200V. The switch is protected by a non-linear varistor (VR) across the switching terminals.

When semiconductor switch (Q₁) is opened, diode (D₁) becomes conductive so that the current stored in inductor (L₁) begins to charge capacitor (C₂), and a second inductor (L₂) becomes energized through capacitor C₃. When capacitor C₃ becomes saturated, the current from L₁, L₂ and C₂ begins to flow through the load resistor R₂ (3) and subsequently forms a high-voltage pulse therein.

When semiconductor switch (Q₁) is turned on, the energy (E=½L₁I₁ ²) is stored in inductor L₁. When semiconductor switch (Q₁) is turned off, energy (E=½C₃V²) is transferred and stored in capacitor C₃. Here, when the voltage at C₃ reaches a specific value, capacitor C₃ is saturated and its capacitance C₃ is reduced to C₃′ so that the voltage across capacitor C₃ is increased from V={square root over (2E/C₃)} to V′= {square root over (2E/C₃′)}. Because the saturation of capacitor C ₃ proceeds in a very short period of time, a compression effect on the pulse results, which in turn applies a short pulse voltage to a load connected in parallel with capacitor C₃.

Waveforms of the output voltage and the current through inductor L₂ in an unloaded state are shown in FIG. 2. In FIG. 2, an upper waveform (CH3) is a waveform of the output voltage, and a lower waveform (CH1) is a waveform of the current in inductor L₂. In the Figure, it could be recognized that the energy is transferred back and forth as between the capacitor and the inductor from the point when semiconductor switch (Q₁) is turned off. In an unloaded state, there is little energy consumption so that the waveform of an oscillation state is shown when the semiconductor switch (Q₁) is turned off.

Waveforms of an output voltage and the current in L₂, with a high-voltage discharge lamp as a load, are shown in FIG. 3. When a load is provided, a pulse form is obtained, which is different from the oscillation-type waveform of the unloaded circuit.

Waveforms of the voltage across the load and the current in inductor L₂ when a 50Ω resistor is used as a load are shown in FIG. 4.

FIG. 5 shows voltage at C₂ and the current stored in inductor L₁. It can be recognized in the Figure that the voltage of C₂ does not exceed 1,200V after the semiconductor switch (Q₁) is turned off. The repetition rate goes up to 50 Hz, which is limited only by the charging source.

FIG. 6 shows a circuit diagram of a stacked pulse generator using several semiconductor switches (Q₁) connected together. The stacked pulse generator is used to accomplish a higher amplitude in output voltage than could be obtained using only one semiconductor switch (Q₁). Three identical pulse generators operating under a common load (i.e., with their outputs connected in series) are connected in parallel. The respective three semiconductor switches (Q₁, Q₂ and Q₃) are driven simultaneously by a common controller (2).

An output voltage waveform for the circuit described above is shown in FIG. 7. As shown in the Figure, the total output voltage is less than three times the output of the respective pulse generator. The maximum unloaded output voltage was 6.3 kV, and the pulse width was 0.9 is (at half amplitude). This results from differences in the parameters of components in the respective pulse generators.

Although various embodiments according to the present invention have been described above, the present invention is not limited to those embodiments. For example, the specific values for the components used may be appropriately adjusted to obtain a desired pulse width or output voltage. In addition, for the non-linear capacitor, any capacitor wherein capacitance is significantly decreased at or above a certain voltage may be used.

By using a non-linear characteristic of a capacitor, it is possible to provide a high-voltage pulse generating device using a semiconductor switching device, which has a small size with high efficiency. In addition, the present invention provides a high-voltage pulse generating device using a semiconductor switching component, which does not use a pulse transformer or a magnetic pulse compressor. 

What is claim is:
 1. A high voltage pulse generating device comprising: a semiconductor switch having an input terminal connected to a first output terminal of a DC power supply; a primary inductor connected between an output terminal of said semiconductor switch and a second output terminal of said DC power supply; a diode having a cathode connected to the output terminal of said semiconductor switch; a capacitor connected between an anode of said diode and the second output terminal of said DC power supply; a secondary inductor having a first terminal connected to the anode of said diode; a non-linear capacitor connected between a second terminal of said secondary inductor and the second output terminal of said DC power supply.
 2. A high voltage pulse generating device according to claim 1, wherein said non-linear capacitor is a ceramic capacitor.
 3. A high voltage pulse generating device according to claim 1, wherein said non-linear capacitor is a BaTiO₃ ceramic capacitor.
 4. A high voltage pulse generating device comprising: a plurality of pulse generating parts connected in parallel to a DC power supply, said pulse generating parts comprising: a semiconductor switch having a first terminal connected to a first output terminal of the DC power supply; a primary inductor connected between an output terminal of said semiconductor switch and a second output terminal of said DC power supply; a diode having a cathode connected to the output terminal of said semiconductor switch; a capacitor connected between an anode of said diode and the second output terminal of said DC power supply; a secondary inductor having a first terminal connected to the anode of said diode; and a non-linear capacitor connected between a second terminal of said secondary inductor and the second output terminal of said DC power supply; wherein said non-linear capacitors of said plurality of pulse generating parts are serially connected.
 5. A high voltage pulse generating device according to claim 4, wherein said non-linear capacitor is a ceramic capacitor.
 6. A high voltage pulse generating device according to claim 4, wherein said non-linear capacitor is a BaTiO₃ ceramic capacitor.
 7. A method of generating a high voltage pulse across a load comprising: drawing current through an inductor; and opening a semiconductor switch to redirect said current through a second inductor and a non-linear capacitor in parallel with said load; wherein saturation of said capacitor causes a current to flow through said load, thereby generating a high voltage pulse thereacross.
 8. The method of claim 7 wherein said non-liner capacitor is a ceramic capacitor.
 9. The method of claim 7 wherein said non-liner capacitor is a BaTiO₃ ceramic capacitor. 